The present invention relates to a binocular.
A conventional binocular includes two telescope systems that have parallel optical axes, an interpupillary adjustment mechanism, a focus adjustment mechanism, a magnifying-power-varying mechanism, and a diopter correction mechanism.
The conventional interpupillary adjustment mechanism is provided so that the left and right telescope systems are rotatable about a shaft provided to the center of the left and right telescope systems.
Conventionally, the magnifying-power-varying mechanism includes a lens group designated as a magnifying-power-varying lens group provided in the left and right telescope systems and operates to move the magnifying-power-varying lens groups along the optical axes thereof The magnifying-power-varying lens groups are moved by driving members provided in the left and right telescope systems.
Since the interaxial distance between the left and right telescope systems is varied by the interpupillary adjustment, in order to simultaneously vary the magnification power of both the left and right telescope systems, the driving members are connected by a connecting member, such as string. A magnifying-power-varying activator, for example a knob, is provided on one of the telescope systems, usually on the right telescope system, to allow the user to actuate the driving members. The operation of the magnifying-power-varying activator moves the right driving member, and the movement of the right driving member is transmitted to the left driving member by the connecting member.
However, if the magnifying-power-varying activator is provided on the right viewer portion, it is inconvenient for a left-handed user. A binocular should be easily operated by both right-handed and left-handed users.
Further, in a conventional binocular the driving members and connecting member are arranged in a complicated manner using pulleys or the like, which makes the assembly of the binocular complicated. Also, often there is a difference between the axial position of the driving members and the axial position of the connecting member, such that the connecting member is not perpendicular with respect to the rotation axes of the driving members. In such an arrangement, the connecting member may not move smoothly and has a greater potential to bind or fail. Accordingly, a simple means of synchronizing the movement of both driving members and therefore both magnifying-power-varying lenses is desirable.
Furthermore, conventionally, the position of the magnifying-power-varying lenses with respect to the rotation of the driving members is not adjustable. Therefore, a binocular wherein the position of the magnifying-power-varying lenses with respect to the driving members can be adjusted is desirable.
Conventionally, the driving members for the magnifying-power-varying mechanism are cam rings and guide rings. In such an arrangement, lens frames that support the magnifying-power-varying lenses include cam pins, and each cam pin is inserted through both a guide groove on the guide ring and a cam groove on the cam ring. If an excessive driving force is applied to the cam pins, the lens frames may break. Accordingly, a binocular must be designed to prevent the lens frames from breaking when an excessive force is applied to the cam pins.
Further, in a conventional binocular, if there is a difference between the visual fields seen through the left and right telescope systems, because of a lens mounting error or the like, the replacement of the faulty lens is necessary. Accordingly, a binocular wherein the position of an improperly mounted lens can be adjusted to correct for a difference between the visual fields of the telescope systems is desirable.
A conventional binocular also has adjustable eye cups, which are slidable between a projected position and a retracted position. A spectacle-wearing user can use the binocular with the eye cup retracted, allowing the spectacle lenses to be closer to the telescope systems. The eye cups have a locking mechanism to keep them in position, generally including two holes formed on the eye cup and one protrusion formed on the viewer portion, such that the protrusion locks into one of the two holes for each position. However, if too much force is applied to the eye cup this locking mechanism is unstable and the eye cup can be accidentally moved from the extended position to the retracted position.
Conventionally, the end surface of an eyepiece frame that is facing the user has a flat cross-section such that a further problem is that, if the user wears spectacles, the curvature of the spectacle lenses may interfere with the flat end surface of the eyepiece frame.